PROJECT SUMMARY Alzheimer?s disease (AD) is a progressive neurodegenerative disorder, accounting for 60?80 % of dementia cases. Aging is the leading risk factor for AD; however, the mechanisms linking aging to the pathogenesis of AD remain elusive. Aging exerts profound impacts on peripheral tissues and brain. The dysfunctional crosstalk between peripheral systems and brain during aging may play a role in the pathogenesis and progression of AD. Advancing age induces adipose tissue dysfunction that drives metabolic decline and systemic inflammation and causes dysregulated production of neuroprotective adipokines and proinflammatory cytokines, which may accelerate brain aging and the onset or progression of AD. We found that aging increases expression of histone deacetylase 9 (HDAC9), an endogenous repressor of adipogenic differentiation, in human and mouse adipose tissue, but decreases HDAC9 expression in the brain. Our findings suggest that HDAC9 in adipose tissue and brain has distinct roles in mediating aging-related effects. We propose to determine 1) the impact of adipocyte HDAC9 on aging- and AD-related metabolic and inflammatory profiles, neuropathology and cognitive impairment; 2) the functional role of HDAC9 in hippocampal and cortical neurons in age- and AD-related neuropathological and cognitive phenotypes; and 3) the mechanisms underlying age- and AD-associated changes in HDAC9 gene expression in adipose tissue and brain.